FR3039149A1 - POROUS CERAMIC MATERIAL OBTAINED BY WEAVING AND ACOUSTIC PANEL COMPRISING SUCH A MATERIAL - Google Patents

Abstract

The invention relates to a porous body (9) made of a ceramic matrix composite material for an acoustic attenuation panel, comprising a plurality of interleaved ceramic fibers (13) and a ceramic matrix (15). The porous body of the invention is remarkable in that it comprises a plurality of channels (17, 18, 22) interwoven with said ceramic fibers and interconnected between them, said channels defining at least one cavity (19a, 19b, 21, 23, 25). The invention also relates to an acoustic attenuation panel comprising such a porous body and an aircraft propulsion unit comprising such a panel. The invention finally relates to a method of manufacturing a porous body of ceramic matrix composite material.

Description

The present invention relates to the field of acoustic attenuation panels in particular for equipping the hot zones for ejecting gases from an aircraft turbojet engine. More specifically, the invention relates to a porous body of ceramic matrix composite material for sound attenuation panel. The invention also relates to an acoustic attenuation panel comprising such a porous body, and to an aircraft propulsion assembly comprising such a panel. The invention finally relates to a method of manufacturing a porous body of ceramic matrix composite material.

As is known per se, the aerodynamic surfaces near the ejection of hot gases from a turbojet engine and which guide the aerodynamic flows are subjected to high temperatures of up to 600 ° C to 1000 ° C.

To help reduce the noise emitted by the turbojet engine in operation, these surfaces are also provided with acoustic attenuation devices in the form of porous surfaces associated with resonant cavities.

Such parts are generally made of metal structures including titanium alloy base or nickel, which makes them heavy.

Such parts can be made using ceramic matrix composite sandwiches, for example according to document WO 2014/118216. However, these processes are very expensive, particularly because of the densification operations in the vapor phase.

The present invention aims at overcoming the drawbacks of the prior art, and relates for this purpose to a porous body made of a ceramic matrix composite material for an acoustic attenuation panel, comprising a plurality of intertwined ceramic fibers and a ceramic matrix, which is remarkable. in that it comprises a plurality of channels intertwined with said ceramic fibers and interconnected with one another, said channels defining at least one cavity.

According to optional features of the porous body according to the invention: the channels are oriented in different directions, in particular in the weft direction and / or in the warp direction of the ceramic fibers; at least one channel is wrapped around a ceramic fiber; at least one ceramic fiber and at least one channel are twisted together; at least one ceramic fiber has a titre of between 50 grams / 1000 meters and 2500 grams / 1000 meters for densities of between 2.2 and 4; at least one channel has a small axis ovoid section of between 0.05 mm and 5 mm and a major axis of between 0.05 mm and 10 mm; the volume ratio of the channels of the porous body is between 2% and 95% of said body, preferably between 50% and 90%; the porous body according to the invention comprises at least one aeroacoustic surface and at least one channel interconnected with at least one cavity with said at least one aeroacoustic surface.

The present invention also relates to an acoustic attenuation panel, comprising: - an inner layer, - an outer layer having an acoustic permeability and intended to come into contact with an airflow to be attenuated acoustically, - an intermediate layer between the layers internal and external, said panel being remarkable in that at least one of the intermediate or outer layers comprises a porous body according to the invention.

In a first variant, the acoustic attenuation panel of the invention is remarkable in that the outer and inner layers belong to the porous body according to the invention.

In a second variant, the acoustic attenuation panel of the invention comprises: - an inner layer, - an intermediate cellular layer, and an outer layer adjacent to the cellular intermediate layer and having an acoustic permeability, intended to come into contact with an airflow to be attenuated acoustically, said panel being remarkable in that said outer layer comprises a porous body according to the invention. The invention further relates to a method of manufacturing a porous body of ceramic matrix composite material comprising the following steps for: - weaving a preform by means of ceramic fibers and fibers of fugitive material; - drape the preform on a tool; - sintering the assembly, at a temperature to remove the fugitive material fibers, so as to form a plurality of channels interwoven with the ceramic fibers and interconnected with each other, said channels defining at least one cavity.

According to an optional feature of the manufacturing method of the invention, the preform comprises: a plurality of warp fibers at least one of said fibers is a warp fiber and at least one of said fibers is a fleece of fugitive material, and / or - a plurality of weft fibers of which at least one of said fibers is a weft ceramic fiber and at least one of said fibers is a fugitive material fiber.

According to optional features, the method comprises, after the draping step and before the sintering step, the steps of: dispersing ceramic powders between the ceramic fibers and the fibers of fugitive material, or infiltrating ceramic powders or a preceramic matrix between the ceramic fibers and the fibers of fugitive material by means of a liquid medium; - Dry and / or polymerize the assembly consisting of the preform and the ceramic powders or the preceramic matrix.

According to optional features, the method comprises, before the draping step, the step of impregnating the ceramic fibers of ceramics or preceramic matrix.

According to optional features, the preform is made partially or entirely by depositing ceramic fibers and fugitive material fibers by implementing an automated draping method.

According to another optional feature, at least one ceramic fiber and at least one fugitive material fiber are twisted together.

According to yet another optional feature, at least one fugitive material fiber is wrapped around a ceramic fiber.

The fugitive material of the fugitive material fibers comprises: one or more materials chosen from thermoplastic plastics and thermosetting plastics, or a metal with a low melting point, in particular lower than the sintering temperature, such as lead , tin aluminum. The invention also relates to an aircraft propulsion unit (that is to say the assembly formed by a turbojet engine equipped with a nacelle, the assembly being able to include the engine pylon), the propulsion unit comprising at least one minus an acoustic attenuation panel as defined above and / or obtained by the method defined above. Other features, objects and advantages of the present invention will appear on reading the description which follows and on examining the appended figures in which: FIG. 1 schematically illustrates an acoustic attenuation panel according to the invention; FIG. 2a is a cross sectional view of the acoustic attenuation panel of FIG. 1 according to a first embodiment of the invention; FIG. 2b is a cross-sectional view of the acoustic attenuation panel of FIG. 1 according to a second embodiment of the invention; FIG. 2c is a cross-sectional view of the acoustic attenuation panel of FIG. 1 according to a third embodiment of the invention; FIG. 3 is an isometric view of a porous body according to the invention; FIG. 4 is an isometric view of a woven preform intended to form a porous body according to the invention; FIG. 5 illustrates an alternative arrangement of a fiber made of fugitive material and a ceramic fiber; FIG. 6 illustrates another alternative arrangement of a fiber made of fugitive material and a ceramic fiber; - Figures 7 to 10 are sectional views along the lines VII-VII, VIII-VIII, IX-IX and X-X of Figure 3.

Throughout the figures, identical or similar references represent identical or similar organs or sets of members.

Referring to Figures 1, 2a, 2b and 2c. The acoustic attenuation panel 1 can equip one or more components of an aircraft turbojet engine nacelle. The acoustic attenuation panel may in particular be installed on any component located in a hot zone of a propulsion unit, such as the ejection cone ("plug" in English terminology) of the turbojet engine hot gases, the structure fixed inner shell of the nacelle (IFS for "inner fixed structure" or IFD for "inner fixed duct" in English terminology) which channels the secondary flow around the hot body of the engine, the flow mixer duct (MFN for "mixed fan" nozzle "in English terminology) and more generally any component of the propulsion unit (including the turbojet engine, the nacelle, and the engine pylon) intended to attenuate a noise level and in a hot zone-that is to say exposed to temperatures above 300 ° C.

The acoustic attenuation panel 1 comprises an outer layer 3 which comes into contact with an acoustically attenuated air flow when the panel equips a nacelle component, an intermediate layer 7 intended to absorb the acoustic energy, and an inner layer 11 acoustically substantially impervious to a waterproof surface preventing the free propagation of waves and positioned to take the intermediate layer 7 sandwiched with the outer layer 3.

FIG. 2a shows in section a first acoustic attenuation panel configuration according to the invention, comprising an outer layer 3 having an acoustic permeability obtained thanks to a plurality of perforations 5, communicating with the intermediate layer 7 constituted by a porous body 9 according to the invention realizing the acoustic attenuation of the panel.

FIG. 2b shows an acoustic attenuation panel alternative according to the invention comprising an inner layer 11 and an outer layer adjacent to said inner layer, coming into contact with an airflow to be attenuated acoustically when the panel equips a component of nacelle and having an acoustic permeability obtained through the porous body 9 according to the invention, performing the acoustic attenuation of the panel. The nature and characteristics of the permeability changing according to the thickness, the outer layer 3 in direct contact with the acoustic flow has a specific porosity and permeability to capture a portion of the acoustic flow. The intermediate layer 7 has a porosity for damping the acoustic wave.

FIG. 2c shows another acoustic attenuation panel alternative according to the invention in which the porous body 9 forms the outer layer 3 of thickness close to the surface and whose permeability is chosen so as to capture the acoustic flux.

Referring to FIG. 3 illustrating the porous body 9 equipping the panel 1. More particularly, FIG. 3 and FIGS. 7 to 10, describe a woven material suitable for producing the variant according to FIG. 2b of porous body according to the invention. .

The porous body 9 is of the ceramic matrix composite material type, for example a metal oxide ceramic matrix. Advantageously, the matrix may comprise at least two different ceramic materials. The local characteristics of the matrix are thus adapted according to the constraints.

The porous body 9 comprises a plurality of ceramic fibers 13 which may be non-limitingly constituted by a material based on metal oxide, alumina, aluminosilicates, whether or not charged, alkali metal oxides, alkaline earth oxides or of zirconia.

The porous body 9 comprises ceramic warp fibers 13a and weft ceramic fibers 13b.

The porous body 9 comprises a matrix 15 (visible in FIGS. 7 to 10) bonding the ceramic fibers to one another, obtained by sintering metal oxide powders, alumina or aluminosilicates with or without charge.

According to the invention, the porous body 9 comprises a plurality of channels 17 or tunnels, interwoven with the ceramic fibers 13. The channels 17 are interconnected with each other. The network of interconnected channels 17 defines one or more cavities or cavernous volumes conferring the desired porosity to the body 9. The porosity imparted to the body 9 by the channels 17 attenuates the noise when the body is or is part of a acoustic panel.

With reference to the acoustic panel variant according to FIG. 2b or 2c, the porous body 9 comprises a plurality of channels 18 arranged to communicate with the upper surface 20 of the porous body 9 at so-called "aero-acoustic" surfaces 181 . These aero-acoustic surfaces 181 constitute openings of the porous material with the acoustic flux to be attenuated and realize via the channels 18 interconnections with the channels 17 of the porous body 9 and with the upper face 20 of the porous body 9. The channels 17 and 18 are obtained by the manufacturing method according to the invention described below.

The method of manufacturing the porous body according to the invention comprises a first step for weaving a preform 90. The preform 90 is shown in FIG. 4. The preform 90 is obtained by a braiding weaving method known to those skilled in the art. , thanks to a loom not shown.

The woven preform 90 comprises ceramic warp fibers 13a and weft ceramic fibers 13b.

The term "ceramic fibers" here defines strands constituted by a set of filaments, the number of filaments per strand being between about 200 and about 10,000 filaments. For metal oxides having a density of between 2.2 and 4, ceramic fibers are preferably chosen whose weight is between 50 grams / 1000 meters and 2500 grams / 1000 meters, and have good weaving properties. For example, for alumina oxide fibers, fibers produced by the company 3M and marketed under the trade names Nextel can be used. It will be possible to use fibers of different grades having different densities, such as Nextel 312 of density 2.7, Nextel 440 of density 3.05, Nextel 550 of density 3.03, Nextel 610 of density 3.9, Nextel 720 of density 3.4.

According to the invention, the ceramic fibers 13 of the preform are interlaced with fibers 170 of a so-called "fugitive" material. The fugitive material fibers 170 are interconnected with each other.

In the present application, the term "fugitive material" means a material capable of being at least partially, and preferably completely removed by heat treatment during the implementation of the method of manufacturing the porous body. During the heat treatment applied, the action of the temperature leads to the elimination of the fugitive material fibers, in particular by oxidation, combustion, melting, evaporation, or sublimation.

The term "fugitive material fiber" defines a wick made of several filaments of fugitive material. The term "fugitive fiber material" may also define a wick made of monofilaments or monofilaments.

A fugitive material fiber 170 may, by way of non-limiting example, consist of one or more immiscible materials with metal oxide powders, alumina or aluminosilicates, whether or not charged, constituting the matrix of the porous body ( after sintering of these powders). The fugitive material is chosen to be destroyed during the sintering step of the powders. By way of example, the fugitive material comprises one or more materials chosen from thermoplastic plastics (such as polyethylene), thermosetting plastics (for example epoxy-based), and low-melting metals ( for example based on aluminum, tin or lead).

A fugitive material fiber 170 may also be constituted by a metal assembly having a melting point less than or equal to the temperature applied for sintering the powders. These materials can be alloys based on lead, tin or aluminum. In the case of metal fibers, they are chosen limited section, to be flexible enough to be woven or draped with ceramic fibers. The fugitive material fiber is then destroyed, when the temperature rise of the assembly for sintering the powders is operated, when the melting temperature of the fugitive material is reached.

The preform of the acoustic panel according to the invention can also be obtained by depositing fibers using a machine according to the known methods of automatic draping (in particular the methods known by the name of AFP for "Automated Fiber Placement"), or filament winding, the machine can then file according to different orientations and sequences of stacks and crossings and with the aid of suitable devices, ceramic fibers and / or fibers of fugitive material or the variants of combinations between ceramic fibers and fibers of fugitive material.

Thus according to the invention, there is obtained a ceramic ceramic porous ceramic composite, the ceramic fibers are continuous within the porous or cavernous structure. The composite material produced then has a structural strength which is directly dependent on the interlacing of the fibers with each other Unlike conventional processes in which the acoustic openings are created by mechanical perforation and removal of material, and thus by cutting the fibers around the acoustic bores, the present invention preserves the continuous fibers while providing acoustic porosity. Thus, the structure according to the invention does not have fibers interrupted or cut near the free edges of the acoustic holes (which are usually areas of crack initiation). The structure according to the invention is therefore more robust than the known structures.

As illustrated in Figure 4, the ceramic fibers or fugitive material of the preform have a substantially ovoidal section. The small axis of the ovoid may be between 0.05 mm and 5 mm and the major axis may be between 0.05 mm and 10 mm.

Of course, any other form of section may be envisaged, such as circular, elliptical, rectangular, etc.

The fugitive material fibers 170 may be arranged substantially co-linear with the warp fibers 13a and / or the weft fibers 13b, i.e. they are woven or arranged in directions similar to the weaving directions and of deposit that the ceramic fibers with which they are associated ..

According to another variant shown in FIG. 5, a fugitive material fiber 170 may be wrapped around a ceramic fiber 13, that is to say that a fiber of fugitive material defines a spiral around a ceramic fiber 13. Preferably, one chooses on the one hand a wick section of ceramic fibers between 0.2 mm and 10 mm, on the other hand a channel section wrapped around the ceramic fiber between 0.02 mm 2 and 0, 5mm ^ and furthermore, a winding ratio 1 turn for 1.5 times the guiped channel section, 1 turn for 3 times the guiped channel width. For a fabric layer made with such gimped fibers, channels of small cross sections are obtained, and porosities generally less than 15%, or even less than 5%. This configuration is particularly advantageous for creating acoustically permeable layers such as the outer layer 3 of the acoustic panel according to the invention. It offers a suitable acoustic opening, with small orifices, which penalizes less the aerodynamic performance of the surfaces subjected to such flow. This configuration can also be used at the intermediate layer 7 of the acoustic panel according to the invention to create an inner layer very thin permeability, for example to create an attenuator dual attenuation capacity. This arrangement can be made especially or part of the fibers of the preform.

According to another variant shown in Figure 6, a ceramic fiber 13 and a fugitive material fiber 170 may be twisted together. Preferably, a section ratio is selected between the wick of ceramic fibers and the twisted cavity of between 0.5 and 2, and a section of ceramic fiber of between 0.2 mm and 10 mm. still another, a twist ratio of between 3 turns per meter and 50 turns per meter. It is also possible to combine in the twisted assembly one or more ceramic fibers with one or more twisted cavities. This arrangement makes it possible in particular to produce a more diffuse or continuous porosity in the same unit of volume and a more diffuse or continuous distribution of fibers and porosities in the same unit of volume. For the same unit of volume, the number of independent locks used for weaving or draping the preform is also reduced, which reduces the cost of obtaining the preform.

This arrangement can be performed on all or part of the fibers of the preform.

The section or arrangement of the fugitive material 170 of the preform 90 gives the channels 17 the same section or arrangement in the porous body 9 when the fugitive material fibers 170 are removed.

When the step of weaving the preform 90 is completed, the method of manufacturing the porous body according to the invention comprises a second step for draping the preform 90 on a tool.

As a variant of the two preceding steps, the ceramic fibers and the fibers in fugitive material are draped by a fiber-depositing or filament winding method, directly on the tooling or on a specific form, and then placed on the molding tooling. .

The third step of the process of the invention then consists in dispersing metal oxide powders between the ceramic fibers and the fibers of fugitive material.

Alternatively, the third step of the manufacturing process may include infiltrating metal oxide powders between the ceramic fibers and the fugitive material fibers by means of a liquid medium.

Alternatively the step of dispersing the matrix in the different inserts of the fibers is performed before the draping of the preform. It is said that the fibers are "pre-impregnated", the matrix being at this stage in the form of ceramic powders, ceramic powder in solution or solutions of preceramics.

A fourth step of the manufacturing process of the invention consists in drying the assembly consisting of the preform and the ceramic powders or the preceramic solution.

The consolidation of the ceramic composite material according to the invention is finally carried out by heating the assembly to a sintering temperature of the constituents of the ceramic or preceramic matrix. The sintering temperature is typically between 1000 ° Celsius and 1600 ° Celsius, more particularly between 1200 and 1300 ° Celsius. This makes it possible to consolidate the matrix and to bond the ceramic fibers together via the matrix.

Furthermore, the method of the invention comprises a step of removing the fugitive material fibers so as to form a plurality of channels intertwined with the ceramic fibers and interconnected with each other, said channels defining at least one cavity.

This step is performed either during the sintering of the assembly when the fugitive material fibers consist of an assembly of polymers such as those previously defined.

This step can also be performed before reaching the sintering temperature, when the fugitive material fibers are constituted by a previously defined metal assembly having a melting point lower than the sintering temperature.

Referring now to Figures 7 to 10, showing an example of porous body 9 seen in section along the lines VII-VII, VIII-VIII, IX-IX and XX of Figure 3, obtained after implementation of the method of manufacture of the invention.

In FIG. 7 is illustrated the porous body 9, comprising a plurality of ceramic warp fibers 13a and weft 13b interleaved with channels 17 in the weft direction, channels obtained by heat treatment of the fibers of fugitive material applied to the preform. during the process of manufacturing the porous body. The channels 17 define a plurality of cavities 19a, 19b of the body 9, conferring porosity to said body.

In FIG. 8 is illustrated the porous body 9 on which we note the cavities 19a, 19b in the weft direction as well as seven channels 22 in the direction of the chain, obtained by heat treatment of seven fibers of fugitive material arranged in the sense of the chain. The channels 22 here define cavities 21 in the direction of the chain, in addition to the cavities 19a, 19b in the direction of the frame. The acoustic permeability of the porous body 9 with the aeroacoustic flow is obtained by the channel 18 which is on the one hand connected with the cavity 19b and which on the other hand has an aero-acoustic surface 181 communicating with the upper surface of the Porous body 9. In FIG. 9, the same cavities 19a, 19b in the weft direction of the porous body 9 are visible, and four channels 22 in the warp direction, obtained by heat treatment of four fibers of fugitive material arranged. in the sense of the chain are illustrated.

These channels 22 here define cavities 23 in the direction of the chain, in addition to the cavities 21 in the direction of the chain and the cavities 19a, 19b in the direction of the frame.

In FIG. 10, the same cavities 19a, 19b in the weft direction of the porous body 9 are visible, and seven channels 22 in the warp direction, obtained by heat treatment of seven fibers of fugitive material arranged in the direction of the chain are illustrated.

These channels 22 here define cavities 25 in the direction of the chain, in addition to the cavities 21 and 23 in the direction of the warp and the cavities 19a, 19b in the weft direction.

In FIG. 10, on the other hand, a cavity 18 reproduces an acoustic permeability with the upper surface 20 of the porous body, being connected on the one hand with at least one cavity 19a or 19b, and on two aero-acoustic surfaces 181 communicating with the upper surface of the porous body 9. The set of cavities 19a, 19b, 21, 23 and 25 defines a porosity network of the body 9, giving the body 9 acoustic attenuation properties. By way of nonlimiting example, the volume ratio of the cavities 19a, 19b, 21, 23 and 25 varies between 5% and 95% of the body, preferably between 50% and 90 °.

In the example described in FIGS. 3, 7 to 10, it is also possible to observe an upper zone of the preform having a limited porosity, corresponding to the outer layer 3 of the acoustic panel. In particular, in FIGS. 8 and 10, the channels 18 in the warp direction are interlaced so as to follow the free surface of the panel at 181, conferring the acoustic permeability of this surface. The intermediate layers of the preform, corresponding to the intermediate layer 7 of the acoustic panel, comprise a much larger proportion of cavities. And finally the lower zone, corresponding to the inner layer 11 of the acoustic panel, has no cavities. The arrangement of the ceramic fibers and the geometric distribution of the preceding cavities have been given solely by way of illustrative example of the invention, the porous body according to the invention being in no way limited to the foregoing examples.

It is in particular envisaged to provide in the porous body according to the invention a zone devoid of channels on a thickness of the preform, which allows to define within the porous body a substantially sealed zone preventing the free propagation of sound waves.

It is also planned to vary the titles of the fibers used and the interlacing patterns, either according to the thickness layers of the preform, or distributed by zones of the preform. This makes it possible to vary the acoustic porosity within a layer of thickness or between the different layers of thickness, and thus to treat different ranges of acoustic frequencies.

As previously indicated with reference to FIG. 2a, the porous body thus produced can be assembled with the inner layer 11 consisting essentially of a sealed surface preventing the free propagation of the waves, and with the outer layer 3 having an acoustic permeability obtained thanks to a plurality of perforations 5 communicating with said porous body 9. By way of example, the surface communication rate of the perforations 5 of the outer layer 3 with the channels 17 of the porous body 9 is between 2% and 20%.

Alternatively, as represented by FIG. 2b, the acoustic panel 1 comprises the tight inner layer 11 and the porous body 9 adjacent to said inner layer 11.

According to a first variant not shown in the figures, the acoustic panel consists of a single preform comprising three layers of thickness in a single constitution: the outer layer 3, the inner layer 11 and the intermediate layer 7.

According to a second variant not shown, the acoustic panel consists of a stack of distinct preforms to create either each of the three layers independently, or two adjacent layers of the panel (the outer layer 3 and the intermediate layer 7, or the intermediate layer 7 and the inner layer 11, in a single preform).

According to a third variant not shown, the porous body is obtained from the successive removal of ceramic fibers and fugitive material in different alternations and different orientations producing an interlacing of ceramic fibers and channels after addition of the matrix, sintering and elimination of fugitive material.

Advantageously, the ceramic fiber preform constituting at least two adjacent layers of the acoustic panel comprises ceramic fibers belonging to both of these two layers. At least one ceramic fiber is interlaced with at least one ceramic fiber of the outer layer 3 (respectively of the intermediate layer 7) with at least one ceramic fiber of the intermediate layer 7 (respectively of the inner layer 11). The two adjacent layers of the panel are then mechanically bonded by ceramic fibers. The structure is therefore more robust, and will be more resistant to damage and the risk of delamination.

In another embodiment, FIG. 2c shows an acoustic panel consisting of an inner layer 11 impervious to the free propagation of the acoustic waves, an intermediate layer 7 constituted by a cellular core, and an outer layer 3 made according to a method. embodiment according to the invention. The cellular core and the inner layer are made of materials and methods known to those skilled in the art, such as laminate for layer 11 and a metal or ceramic honeycomb type material for layer 7. layer 3 according to the invention is for example glued to the layer 7 by a ceramic adhesive. The cavities of the preform 9 according to the invention have an acoustic permeability of between 3 and 20%, channels 18 in the preform 90 provide the interconnection between the aero acoustic surfaces 181 of the upper surface and the cavities of the core. alveolar.

It is also envisaged to use ceramic fibers with fugitive material wrapped around the variant of FIG. 5, to obtain low levels of porosity through a layer while having a more uniform distribution. In particular for the surface layers of the outer layer 3, and in particular the aero-acoustic surface layer, this configuration has very small unitary interconnection surfaces. The drag induced on the aerodynamic flow is reduced.

It is also envisaged to use ceramic fibers with fugitive material covered, to create an intermediate layer of fabric within the thickness of the intermediate layer 7, to create an intermediate microporous septum. Thanks to such an arrangement, it is possible to create in the thickness of the panel two sub-areas of acoustic attenuation conjugate.

It is also envisaged to make all or part of the porous body 9 according to the invention by automated draping process, consisting of the removal of fibers in layers or sucessive bands and in different orientations on the surface to be molded. The different types of ceramic fibers, fibers of fugitive material, may be used alternately, independently or in combination with guiped or twisted. The ceramic fibers may be pre-impregnated with powders of ceramics or preceramic matrix in viscous form compatible with automated draping processes, making it possible to eliminate or reduce infiltration operations of ceramic powder or preceramic matrix before consolidation. The intertwining of fugitive material fibers according to the different directions and the different successive layers conferring on the structure obtained, after the sintering and fugitive material removal operations, sets of cavities (at least partially) interconnected with one another and conferring the porosity acoustic panel for acoustic attenuation by said panel.

Thanks to the present invention, there is obtained a porous body of ceramic matrix composite material forming all or part of an acoustic attenuation panel having a network of cavities ensuring the acoustic attenuation of the panel.

The acoustic ceramic ceramic matrix material panel is adapted to equip hot areas of a propulsion unit of an aircraft.

In addition, the manufacturing method according to the invention makes it possible to obtain a porous body with communicating cavities in which the acoustic treatment is obtained during the sintering of the assembly. The porous body thus obtained can then be used to form the cellular core and / or the permeable surface of a ceramic acoustic attenuation panel of a turbojet nacelle component.

Claims (20)

A porous body (9) of a ceramic matrix composite material for acoustic attenuation panel, comprising a plurality of intertwined ceramic fibers (13) and a metal oxide matrix (15), characterized in that it comprises a plurality of channels (17, 18, 22) interwoven with said ceramic fibers and interconnected together, said channels defining at least one cavity (19a, 19b, 21, 23, 25). 2. Porous body (9) according to claim 1, characterized in that the channels (17, 18, 22) are oriented in different directions, in particular in the weft direction and / or in the warp direction of the ceramic fibers (13). 3. Porous body (9) according to one of claims 1 or 2, characterized in that at least one channel (17) is wrapped around a ceramic fiber (13). 4. Porous body (9) according to any one of claims 1 to 3, characterized in that at least one ceramic fiber (13) and at least one channel (17) are twisted together. 5. porous body (9) according to any one of claims 1 to 4, characterized in that at least one ceramic fiber (13) has a titer of between 50 grams / 1000 meters and 2500 grams / 1000 meters for densities between 2.2 and 4. 6. Porous body (9) according to any one of claims 1 to 5, characterized in that at least one channel (17) has an oval section of small axis between 0.05 mm and 5 mm and major axis between 0.05 mm and 10 mm. 7. Porous body (9) according to any one of claims 1 to 6, characterized in that the volume ratio of the channels (17) of the porous body is between 2% and 95% of said body, preferably between 50% and 90 %. 8. porous body (9) according to any one of claims 1 to 7 characterized in that it comprises at least one aero-acoustic surface (181) and in that at least one channel (18) interconnects at least one cavity (19a, 19b, 21, 23, 25) with said at least one aero-acoustic surface (181). 9. Acoustic attenuation panel (1), comprising: - an inner layer (11), - an outer layer (3) having an acoustic permeability and intended to come into contact with an airflow to be attenuated acoustically, - a intermediate layer (7) between the inner and outer layers, characterized in that at least one of the intermediate (7) or outer (3) layers comprises a porous body (9) according to any one of claims 1 to 8 . 10. sound attenuation panel (1) according to the preceding claim, characterized in that the outer layers (3) and intermediate (7) comprise a porous body (9) according to any one of claims 1 to 8. An acoustic attenuation panel (1) according to claim 9 or 10, characterized in that at least a portion of the ceramic fibers of the outer layer (3) is interwoven with a portion of the fibers of the intermediate layer (7). and / or characterized in that at least a portion of the ceramic fibers of the inner layer (11) are interwoven with a portion of the fibers of the intermediate layer (7). 12. A method of manufacturing a porous body (9) made of ceramic oxide ceramic matrix composite material comprising the steps of: - weaving a preform (90) by means of ceramic fibers (13) and fibers of fugitive material (170) ); - Draping the preform (90) on a tool; - sintering the assembly at a temperature to remove the fugitive material fibers (170), so as to form a plurality of channels (17, 18a, 18b) interwoven with the ceramic fibers (13) and interconnected between them, said channels defining at least one cavity (19a, 19b, 21, 23, 25). 13. Manufacturing method according to claim 12, characterized in that the preform (90) comprises: a plurality of warp fibers at least one of said fibers is a chain ceramic fiber (13a) and at least one of said fibers is a fugitive material fiber (170), and / or - a plurality of weft fibers of which at least one of said fibers is a weft ceramic fiber (13b) and at least one of said fibers is a fleece of fugitive material (170) ). 14. The manufacturing method according to one of claims 12 and 13, comprising, after the draping step, the steps: dispersing ceramic powders between the ceramic fibers and the fibers of fugitive material, or infiitrer ceramic powders or a preceramic matrix between the ceramic fibers and the fibers of fugitive material by means of a liquid media; drying and / or polymerizing the assembly consisting of the preform and the ceramic powders or the preceramic matrix. 15. Production method according to one of claims 12 to 14, characterized in that the ceramic fibers are impregnated with ceramics or preceramic matrix before the step of draping the preform. 16. The manufacturing method according to one of claims 12 to 15, characterized in that the preform is made partially or entirely by depositing ceramic fibers and fugitive material fibers by carrying out an automated draping process. 17. The manufacturing method according to one of claims 12 to 16, characterized in that at least one ceramic fiber (13) and at least one fugitive material fiber (170) are twisted together. 18. The manufacturing method seion any one of claims 12 to 17, characterized in that at least one fugitive material fiber (170) is wrapped around a ceramic fiber (13). 19. Manufacturing method according to any one of claims 12 to 18, characterized in that the fugitive material comprises: - one or more materials selected from thermoplastic plastics and thermosetting plastic materials, or - a metai having a point of melting lower than the sintering temperature such as a lead-based or tin-based alloy or an aluminum alloy. 20. Aircraft propulsion unit comprising at least one acoustic attenuation panel (1) according to one of claims 9 to 11, and / or at least one acoustic attenuation panel comprising a porous body obtained by a method according to one of claims 12 to 19.